Critical thinking (CT) skills are generally considered to be vital to success at university, but Asian students are sometimes perceived as lacking these skills. This research explores the effect that thinking in a second language has on CT performance. To assess this, two groups of students were tested on a split-test version of the "Watson Glaser Critical Thinking Appraisal[R] Short Form A" in both English and Chinese, one group taking the English half of the test first and the second group taking the Chinese half first. Three participants were also interviewed about the test-taking experience. The findings indicate CT performance is more difficult in an L2: participants who took the English test first performed significantly better when they took the Chinese test second, the group who took the Chinese test first performed significantly better than the group who took the English test first and interviewees reported experiencing the English test as more difficult. (Contains 3 tables and 3 figures.)